vddcore voltage is unstable

[fantasylsdo]

Dears,

I use STM32MP151FAD3 together with STPMIC1. 

Nowdays I monitored the voltage of vddcore and found it's not stable shown as below.

Mostly it's around 1.2v while sometimes it's up to 1.33v .

Referring to documentation, I guess it's casued by dynamic voltage and freqency scaling (DVFS). Is my thought correct? Also, is it a normal scenario? will the ustable vddcore have any inflence on EMC?

[liaifat85]

If DVFS is enabled, please check the configuration settings and thresholds. Adjusting these settings might help stabilize the voltage if necessary.

[fantasylsdo]

Thanks for your reply. How do I know whether DVFS is enabled or not? How to adjust these setting? Do you have any recommendation? 

[PatrickF · Accepted solution]

Hi @fantasylsdo ,

What you see is normal.

Please have a look to https://wiki.st.com/stm32mpu/wiki/How_to_change_the_CPU_frequency#OPP_table_2

I think the transitions recurrence between two OPP are too slow to affect the EMC, but obviously, there could be different spectrum of the emission on each CPU frequency (but usually, board emissions are dominated by external interfaces such as DDR or else).

Regards.